Contaminant pathways in Port Curtis: Final report - OzCoasts

Contaminant pathways in Port Curtis: Final report6: Occurrence of imposexThe life cycle of the gastropod also has a bearing on the impact of TBT at thepopulation level. The decline of N. lapillus in populations severely affected byimposex has been attributed to a reduction in recruitment caused by a decreasein reproductive capacity (Bryan et al. 1986). This gastropod does not have aplanktonic larval stage and apart from the small number of juveniles that may reachother sites via pieces of floating debris, maintenance of a population relies solely onits ability to reproduce. M. marginalba, however, has a long-term planktonic larvalstage (Underwood 1974), allowing recruitment of individuals from other locations.Therefore complete decimation of this species at severely affected sites is unlikely.In conclusion imposex was found to be present in M. marginalba collected fromPort Curtis confirming a sublethal, biological response to TBT exposure. Althoughrelated to shipping intensity, the frequency and grade of the imposex conditionwere not severe in comparison to other port surveys. Due to the mulberry whelks’ability to recruit juveniles from unaffected locations, conservation of the species ishighly likely despite the effects of imposex. Other more TBT-sensitive speciessuch as Thais which have non-planktonic larval stages may be more affected.Some subsequent re-surveying studies (post TBT ban) in Australia have noted anoverall trend for decline in either imposex frequency and/or severity in major portsand coast sites since the introduction of the ban (Gibson & Wilson 2003; Reitsemaet al. 2003). Globally, the condition is likely to slowly improve with the introductionof further restrictions on the use of TBT in 2008.RTVD0.75 mmFigure 6.3. Imposex in M. marginalba with penis bud (arrowed)RT = right tentacle, VD = vas deferens73(Photo courtesy of Leonie Andersen)